Position control for self-loading roll

Abstract

A hydraulic crown support system employs a stationary cross head mounted within a cylinder or beneath an extended nip shoe. Individual hydraulic pistons are disposed along the stationary cross head, which, under the force of hydraulic pressure, support the inner wall of a roll or an extended nip shoe. The displacement of the support cylinders is controlled through one or more adjustable ports formed in the sidewall of the hydraulic cylinder or cylinders which support the roll or extended nip shoe. With a piston which extends from one end of the stationary cross head to the other, some tilting from one side to the other of the cross head can be achieved by the adjustment of the pressure ports, thus compensating for misalignment in the vertical direction between an extended nip or crown-controlled roll.

I claim: 
     
       1. In a papermaking machine having a first cylindrical roll and a nip member supported on a stationary cross head, wherein the nip member engages a paper web between the first cylindrical roll and the nip member, defining a nip therebetween, and a piston mounted within a piston cavity formed in the cross head which is operable to move in a nipwad direction toward and away from the nip, the improvement comprising: a first port extending from the piston cavity through the cross head;   a second port extending from the piston cavity through the cross head, wherein the second port is spaced form the first port away from the nip; and   a valve which is operable to selectively block the first port, wherein hydraulic fluid introduced into the piston cavity may escape from the piston cavity to a low pressure vent area through either the first or the second port depending on the state of the valve when the piston is positioned within the cavity so as to uncover said first or second port, such that the piston may be advanced nipward a limited amount in response to the introduction of hydraulic fluid into the piston cavity.   
     
     
       2. The apparatus of claim 1 further comprising a plurality of piston cavities formed in the cross head, and a plurality of pistons extending therefrom wherein each piston cavity has a first port and a second port formed therein, and a valve which is operable to selectively block the first port. 
     
     
       3. The apparatus of claim 1 further comprising: at least one additional port extending from the piston cavity through the cross head, wherein each additional port is spaced from the second port away from the nip; and   a second valve which is operable to selectively block the second port to provide selected venting of hydraulic fluid so the piston can not extend toward the nip further than the position determined by the selected port.   
     
     
       4. The apparatus of claim 1 wherein the nip member comprises a second cylindrical roll rotatable about the stationary cross head which forms the nip with the first roll. 
     
     
       5. The apparatus of claim 1 wherein the nip member is a concave shoe which forms an extended nip with the first roll. 
     
     
       6. In a papermaking machine having a first cylindrical roll and a nip member supported on a stationary cross head, wherein the nip member engages a paper web between the first cylindrical roll and the nip member, defining a nip therebetween, and a piston mounted within a piston cavity formed in the cross head which is operable to move in a nipward direction toward and away from the nip, the improvement comprising: a first port extending from the piston cavity through the cross head; and   a second port extending from the piston cavity through the cross head, wherein the second port is spaced axially along the cross head form the first port, wherein hydraulic fluid introduced into the piston cavity may escape from the piston cavity to a low pressure vent area through either the first or the second port, when uncovered by the piston, and wherein the piston may be advanced nipward a limited mount in response to the introduction of hydraulic fluid into the piston cavity so the piston in proximity to a port can not move further in a nipward direction than the position determined by said port.   
     
     
       7. The apparatus of claim 6 wherein the nip member comprises a second cylindrical roll rotatable about the stationary cross head which forms the nip with the first roll. 
     
     
       8. The apparatus of claim 6 wherein the nip member is a concave shoe which forms an extended nip with the first roll.